1. Field of the Invention
The present invention relates to a cuff of a blood pressure monitor for measuring the blood pressure as being mounted on the body of a subject, and more particularly relates to a structure of the cuff of a wrist-mount blood pressure monitor used in a wrist-mount blood pressure monitor for measuring the blood pressure on the wrist.
2. Description of the Related Art
Recently, importance of self-control of blood pressure has recognized, and the wrist-mount blood pressure monitor capable of measuring more easily than the brachial type is widely used at home as a household blood pressure monitor. A schematic configuration of a conventional wrist-mount blood pressure monitor 100 is explained by referring to FIG. 12 and FIG. 13. FIG. 12 is a general perspective view showing the appearance of the wrist-mount blood pressure monitor 100, and FIG. 13 is a block diagram showing an internal structure of the wrist-mount blood pressure monitor 100. Referring to both diagrams, the wrist-mount blood pressure monitor 100 comprises a main body 101 incorporating a control device for measuring the blood pressure, and a cuff 102 of a wrist-mount blood pressure monitor which the main body 101 is attached.
A display 103 and a start switch 104 are provided on the outer surface of the main body 101, and a pressure sensor 105, a pressurizing pump 106, an exhaust valve 107, and a CPU 108 for controlling these devices are provided in its inside.
The cuff 102 of wrist-mount blood pressure monitor comprises an air bag 109 for collecting the air sent out from the pressurizing pump 106 and oppressing an artery of the wrist, a band 110 having the air bag 109 disposed at its inner side for mounting on the wrist, and a fastener 111 for winding and fixing the band 110 on the wrist.
Measurement of blood pressure by using the wrist-mount blood pressure monitor 100 having such configuration is explained by referring to FIG. 14 to FIG. 16. In FIG. 14 to FIG. 16, for the sake of convenience, only the cuff 102 of the wrist-mount blood pressure monitor is shown, and the main body 101 is not shown. FIG. 14 is a schematic sectional view of the cuff 102 of the wrist-mount blood pressure monitor along the longitudinal direction before mounting on the wrist, and air is not supplied into the air bag 109 yet. FIG. 15 is a sectional diagram showing a deflated state of the cuff 102 of the wrist-mount blood pressure monitor mounted on the wrist 1. FIG. 16 is a sectional view showing an inflated state of the cuff 102 of the wrist-mount blood pressure monitor mounted on the wrist 1.
The cuff 102 of the wrist-mount blood pressure monitor shown in FIG. 14 is fixed by using the band 110 so that the air bag 109 comes to a position confronting the radial artery 5 and ulnar artery 7 of the wrist 1. Herein, the principal constituents of the wrist 1 include, as shown in FIG. 15, the radius 2 positioned at the thumb side, the ulna 3 positioned as the little finger side, the deep flexor digital tendon 4a and palmar long flexor tendon 4b positioned near the radius 2, the radial artery 5, the superficial flexor digital tendon 6a and ulnar carpal tendon 6b positioned near the ulna 3, and the ulnar artery 7.
When the cuff 102 of the wrist-mount blood pressure monitor is completely mounted on the wrist 1, by supplying air from the pressurizing pump 106 into the air bag 109 as shown in FIG. 16, the radial artery 5 or the ulnar artery 7 (or both) of the wrist 1 is oppressed, and the exhaust valve 107 is released, and in the process of discharging air from the air bag 109, the pressure in the air bag 109 is measured by the blood pressure sensor 105, and the blood pressure measurement data is obtained.
The wrist-mount blood pressure monitor is said to be inferior in precision to the brachial type blood pressure monitor. One of the causes is lack of oppression force on the artery of the wrist. Lack of oppression force on the artery means that the pressure of the vascular inner wall to be measure (hereinafter called vascular inner wall pressure) is smaller as compared with the air bag inner pressure. When the vascular inner wall pressure and air bag inner pressure are equal, by measuring the air bag inner pressure, an accurate vascular inner wall pressure is obtained, so that an accurate blood pressure can be measured.
However, when the oppression force is insufficient, the air bag inner pressure becomes higher than the vascular inner wall pressure, and the air bag inner pressure is directly measured as the blood pressure, so that a higher blood pressure than the actual pressure is measured. One of the causes of such lack of oppression force is lack of oppression width (hereinafter cuff width) in the wrist by the air bag.
The guideline of cuff width of brachial type blood pressure monitor is specified by AHA (American Heart Association), but there is no guideline for the cuff width of wrist-mount blood pressure monitor. Accordingly, the definition of cuff width of the brachial type blood pressure monitor (width of specific multiple of diameter of applicable brachial girth) is directly applied to the wrist. At the present, the cuff width of wrist-mount blood pressure monitor is set at about 50 to 60 mm. If the cuff width of the wrist-mount blood pressure monitor is determined according to this definition, lack of oppression force occurs. One of the causes is that the wrist contains many muscles and tendons not existing in the brachium, and the bones are present relatively near the cuticle, and the oppression of artery by the air bag is impeded.
As shown in a sectional view in FIG. 16, a sufficient air is supplied in the air bag 109, and the air bag 109 is inflated toward the wrist 1 side. However, due to the presence of the radius 2 and palmar long flexor tendon 4b, the inflation of the air bag 109 is impeded, and the radial artery 5 is not oppressed sufficiently, and also the inflation of the air bag 109 is impeded by the presence of the superficial flexor digital tendon 6a and ulnar carpal tendon 6b, and the ulnar artery 7 is not sufficiently oppressed.
If the oppression of artery by the air bag 109 is not impeded at all, as schematically shown in FIG. 17, a specified cuff width W1 can be obtained by sufficiently inflating the air bag 109, but in the presence of the radius 2, palmar long flexor tendon 4b, and others, as schematically shown in FIG. 18, inflation of the air bag 109 is impeded by the presence of the radius 2, palmar long flexor tendon 4b, and others, and hence the cuff width W2 is insufficient.
It is hence a primary object of the invention to present a cuff of wrist-mount blood pressure monitor capable of oppressing the artery positioned at the wrist securely without having effects of muscle, tendon and bone existing in the wrist area.
The cuff of a wrist-mount blood pressure monitor according to the invention comprises an inflatable bag receiving a predetermined amount of a fluid for pressurizing an artery of the wrist, and mounting means for mounting the inflatable bag on the wrist, in which the inflatable bag includes a first inflatable portion, and a second inflatable portion disposed between the first inflatable portion and the wrist, being made of a material having a higher stretchability than the material of the first inflatable portion.
In this configuration, when a fluid is supplied into the inflatable bag, both the first inflatable portion and second inflatable portion are inflated by the supply of the fluid. Since the second inflatable portion is made of a material having a higher stretchability than the material of the first inflatable portion, a specified pressure to the wrist side is assured by inflation of the first inflatable portion. Moreover, the second inflatable portion is inflated in a state of tight contact with the wrist, the second inflatable portion flexibly intrudes into the tendons and bones, so that the second inflatable portion may intrude into the spaces between a tendon and a tendon, between a tendon and a bone, or between a bone and a bone.
Accordingly, regardless of the presence of muscle, tendon or bone in the wrist, it is possible to sufficiently apply a pressure to the artery of the wrist since the pressure from the first inflatable portion is applied to the wrist with which the second inflatable portion comes into contact. As a result, insufficient pressurizing force can be improved, so that it is possible to measure the blood pressure with good accuracy even in a wrist-mount blood pressure monitor.
Owing to these features, as mentioned above, by inflation of the first inflatable portion, a specified pressure to the wrist side is assured, and the second inflatable portion is inflated in a state of tight contact with the wrist, so that the second inflatable portion may flexible intrude into the muscles, tendons and bones.
Further preferably, the shape of the second inflatable portion at the wrist side is formed of extruding portions and dent portions. By the shape of extruding portions and dent portions, a higher expanding and contracting property may be obtained, and intrusion of the second inflatable portion into the muscles, tendons and tone when inflated can be realized more securely.